1. Field of the Invention
This invention relates to a process for the preparation of 3,4-dihydro-2-substituted-4(or 3)-oxo-2H-1,2-thiazine-3(or 4)-carboxylic acid 1,1-dioxide derivatives, valuable intermediates for the preparation of non-steroidal antiinflammatory agents.
More particularly, it relates to the preparation of the aforementioned carboxylic acid magnesium chelate derivatives and its acid by reacting appropriately 3,4-dihydro-2-substituted-4(or 3)-oxo-2H-1,2-thiazine 1,1-oxide compounds with alkylmagnesium carbonates and then hydrolysing the obtained magnesium chelates in the presence of acids respectively and to the their as intermediates for the preparation of N-substituted-4(or 3)-hydroxy-2-substituted-2H-1,2-thiazine-3(or 4-carboxamide 1,1-dioxide derivatives.
2. Description of the Prior Art
The instability of .beta.-keto carboxylic acid represented by the general formula (I) or (II), evidenced by their tendency to undergo decarboxylation and therefore to form a cause of lower yield of the object compound resulting therefrom is well known to those skilled in the art. That is, U.S. Pat. No. 3,892,740, issued on July 1, 1975, described that 3,4-dihydro-4-oxo-2H-1,2-benzothiazine-3-carboxylic acid, 1,1-dioxides have been prepared by hydrolysis of the corresponding ester but decarboxylated rapidly. The observed instability arises from their .beta.-keto structure.
U.S. Pat. No. 4,100,347, issued on July 11, 1978 discloses that the decarboxylation can be avoided by hydrolysis, in the presence of hydroxide ions, of an alkyl ester or aralkyl ester of 3,4-dihydro-2-methyl-4-oxo-2H-1,2-benzothiazine-3-carboxylic acid 1,1-dioxide to form the corresponding 3,4-dihydro-2-methyl-4-oxo-2H-1,2-benzothiazine-3-carboxylic acid 1,1-dioxide.